Human beings are doing unprecedented things to the Earth, which is sort of impressive when you realize that the planet has existed for more than 4.5 billion years. But that’s what happens when 7 billion people produce and consume more and more stuff, emitting enormous amounts of gases like carbon dioxide and generally making of muck of things for everyone else.

Take the oceans. Researchers already know that the seas are becoming more acidic, thanks largely to the increase in the atmospheric concentration of carbon. (Much of the carbon in the air is absorbed by the oceans—think of the fizz in a soda can—which over time makes them more acidic.) Over the last hundred years, the ocean pH—which measures the relative acidity of a liquid—has fallen by 0.1 unit to 8.1 That may not sound like much, but according to a new study published in Science, it’s all but unprecedented. Ocean acidification is now almost certainly occurring faster than it has for at least 300 million years—and as the rate of manmade carbon emissions increases in the future, acidification will likely only accelerate. That will have dire effects on corals and other ocean life that will struggle to adapt to a marine environment that will be changing—by geological standards at least—at breakneck pace.

What we’re doing today really stands out. We know that life during past ocean acidification events was not wiped out — new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about — coral reefs, oysters, salmon.

The Science researchers reviewed hundreds of studies of paleoceanographic studies to try to get a consensus on how the pH levels of the ocean has changed over time. It’s a bit like paleontology—scientists have to look for fossils and other physical proxies to get a sense of how changing carbon levels in the atmosphere has affected the oceans.

The researchers found only one moment in the past when the oceans seemed to be changing anywhere near as fast as they are today. That was the Paleocene-Eocene Thermal Maximum (PETM), which occurred some 56 million years ago. Back in the 1990s, scientists excavated a layer of mud off the seafloor near Antarctica that was traced back to that period. Over the course of 5,000 years during the PETM, carbon levels in the atmosphere doubled for reasons scientists still don’t know. That pushed global temperatures up by 6 C—one of the reasons why the era is called “hothouse Earth,” while the pH of the oceans may have fallen by as much as 0.45 units, becoming significantly more acidic.

More acidic waters are bad news for sea creatures that have carbonate shells, which can simply dissolve if pH levels fall too low. That’s exactly what seemed to happen during the PETM. That brown layer of mud scientists peeled off the seafloor near Antarctica was all that was left of dissolved carbonate plankton shells from the PETM. As many as half of all speceis of benthic foraminifers also went extinct, which may mean that organisms higher up on the marine chain were affected by acidification as well.

That doesn’t bode well for our times. As rapidly as carbon increased and the oceans became more acidic during the PETM, were changing the climate far more quickly now—the current acidification rate is at least 10 times faster than what happened during the PETM. As study co-author Andy Ridgwell of Bristol University puts it, this “raises the possibility we are entering an unknown territory of marine ecosystem change.”

This is what’s so scary about climate change—we are altering the planet at an incredibly rapid rate, faster than almost any analogous historical event. Life can adapt, but the faster the planet changes, the harder it will be for species—including us, potentially—to keep pace. And we have a word for what happens when species can’t keep pace with environmental change: extinction.